Molecular interactions between light and hormone signaling to control plant growth

As sessile organisms, plants modulate their growth rate and development according to the continuous variation in the conditions of their surrounding environment, an ability referred to as plasticity. This ability relies on a web of interactions between signaling pathways triggered by endogenous and environmental cues. How changes in environmental factors are interpreted by the plant in terms of developmental or growth cues or, in other words, how they contribute to plant plasticity is a current, major question in plant biology. Light stands out among the environmental factors that shape plant development. Plants have evolved systems that allow them to monitor both quantitative and qualitative differences in the light that they perceive, that render important changes in their growth habit. In this review we focus on recent findings about how information from this environmental cue is integrated during de-etiolation and in the shade-avoidance syndrome, and modulated by several hormone pathways—the endogenous cues. In some cases the interaction between a hormone and the light signaling pathways is reciprocal, as is the case of the gibberellin pathway, whereas in other cases hormone pathways act downstream of the environmental cue to regulate growth. Moreover, the circadian clock adds an additional layer of regulation, which has been proposed to integrate the information provided by light with that provided by hormone pathways, to regulate daily growth.     

Ionic homeostasis and redox metabolism upregulated by 24-epibrassinolide are crucial for mitigating nickel excess in soybean plants,enhancing photosystem II efficiency and biomass

• Nickel (Ni) excess often generates oxidative stress in chloroplasts, causing redox imbalance, membrane damage and negative impacts on biomass. 24-Epibrassinolide (EBR) is a plant growth regulator of great interest to the scientific community because it is a natural molecule extracted from plants, is biodegradable and environmentally friendly. This study aimed to determine whether EBR can improve ionic homeostasis, antioxidant enzymes, PSII efficiency and biomass by evaluating nutritional, physiological, biochemical and morphological responses of soybean plants subjected to Ni excess.
• The experiment used four randomized treatments, with two Ni concentrations (0 and 200 μm Ni, described as –Ni²⁺ and +Ni²⁺, respectively) and two concentrations of EBR (0 and 100 nm EBR, described as –EBR and +EBR, respectively).
• In general, Ni had deleterious effects on chlorophyll fluorescence and gas exchange. In contrast, EBR enhanced the effective quantum yield of PSII photochemistry (15%) and electron transport rate (19%) due to upregulation of SOD, CAT, APX and POX.
• Exogenous EBR application promoted significant increases in biomass, and these results were explained by improved nutrient content and ionic homeostasis, as demonstrated by increased Ca²⁺/Ni²⁺, Mg²⁺/Ni⁺² and Mn²⁺/Ni²⁺ ratios.

     

Effects of structural analogs of brassinosteroids on the recovery of growth inhibition by a specific brassinosteriod biosynthesis inhibitor

A brassinosteroid inhibitor (Brz2001) was used to block the growth of roots, hypocotyls, and epicotyls of soybean seedlings, producing a dwarf phenotype. The application of 24-epibrassinolide completely reversed the inhibitory effects of Brz2001. Two other growth-promoting brassinosteroid analogs, MH5 and BB6, partially overcame the Brz2001-induced growth defects. The growth inhibition of Brz2001-treated seedlings was more effectively reversed by MH5 than by BB6, which may be due to the structural differences between the two compounds. These results indicate that the studied analogs may show brassinosteroid-like activity and therefore may have some practical use instead of brassinolide or its analogues.     

Biological activities of new monohydroxylated brassinosteroid analogues with a carboxylic group in the side chain

Thirteen monohydroxylated brassinosteroids analogues were synthesized and tested for their biological activity in plant and animal systems. The cytotoxic activity of the products was studied using human normal and cancer cell lines with 28-homocastasterone as positive control, their brassinolide type activity was established using the bean second-internode test with 24-epibrassinolide as standard.     

Application of brassinosteroids to rice seeds (Oryza sativa L.) reduced the impact of salt stress on growth, prevented photosynthetic pigment loss and increased nitrate reductase activity

The effect of applying brassinosteroids to seeds on growth, pigment levels and nitrate reductase activity of rice (Oryza sativa L.) plants grown on saline substratum was investigated. Brassinosteroids reduced the impact of salt stress on growth, considerably restored pigment levels and increased of nitrate reductase activity.